Incandescent electric lamp



May 13, 1941. P. SCHWERIN 2,241,935

INCANDESGENT ELECTRIC LAMP Original Filed March 16, 1936 2 Sheets-Sheet 1 ATTORNEYS.

y 1941- P. SCHWERIN 2,241,935

INCANDESCENT ELECTRIC LAMP Original Filed March 16, 1936 2 Sheets-Sheet 2 INVENTOR.

ATTORNEYJS.

Patented May 13, 14l

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earne Application March- 16, 1936, Serial No. 69,641 Renewed March 30, 1940 8 Claims.

This invention relates to incandescent electric lamps and has for its object a lamp provided with a main and an auxiliary filament in combination with means for automatically substituting the auxiliary filament for the main filament in the event of burning out of the latter.

In an incandescent lamp embodying the invention, three filament supporting. wires are provided, the first and second of which are connected to the usual terminal contacts whilev the third wire has no such connection. The main filament is connected between the first and second wires while the auxiliary filament is connected between the first and third wires. A strip of thermostat metal is attached at one end to the second wire near the point of attachment therewith of the main filament, and is so arranged that when cold it contacts with the third wire but when heated bends out of such contact.

In normal operation of the lamp, heat supplied to the thermostat metal from the main filament causes it to remain out of contact with the third wire so that current passes only through the main filament. However, in case the main filament burns out, such source of heat is destroyed and the thermostat metal moves back into contact with the third wire and closes the circuit through the auxiliary filament. The general heat within the bulb is insuiiicient to operate the thermostat strip which is of sufficiently low resistance that the passage of current therethrough does not heat it appreciably.

Other objects, novel features and advantages of this invention will become apparent from the following specification and accompanying drawings, wherein:

Fig. 1 is a front elevation partly broken away of an incandescent lamp embodying the invention;

Fig. 2 is a side elevation thereof; a

Fig. 3 is a rear elevation of the stem and associated parts with the main filament operative but no current flowing;

Fig. 4 is a view similar to- Fig. 3 with current flowing;

Fig. 5 is a view similar to Fig. 2 of a modifica tion;

Fig. 6 is a front elevation of the stem and associated parts showing a modification with the main filament operative but no current flowing;

Fig. 7 is a section on the line of Fig. 6;

Fig. 8 is a view similar to Fig. 6 with current fiowing, and

Fig. 9 is a section on the line 9-9 of Fig. 8.

A glass bulb iii contains the usual stem l i in 1,..-

which are sealed three supporting wires l2, l3 and it respectively, of which l2 and I3 are connected by suitable leading-in Wires with the usual external contacts of incandescent lamps. A main filament i5 is supported between the upper ends of the wires i2 and it while the auxiliary filament it is supported between the upper ends of the wires l2 and M. A strip of thermostat metal i l is attached at one end to the supporting wire l3 near the point of attachment therewith of the main filament i5 and is arranged. when cold to contact the supporting wire Hi. and when heated to bend out of contact therewith.

When current is first supplied to this lamp, both filaments will be energized but as heat. is communicated to the thermostat strip I1 from the filament it, it will bend out of contact with. the wire it and thus open the circuit through the auxiliary filament It so that only the main filament i5 is energized. Such condition will exist so long as the main filament remains operative. However, if for any reason the main filament becomes inoperative, the source of heat for operating the thermostat strip I"! is destroyed and this strip will move back into contact with the wire i l whereupon the circuit through the auxiliary filament is closed and it becomes energized. This filament, however, does not act as a source of heat for operating the strip l-l since the point of contact with such strip with the supporting wire is spaced at considerable distance from the point of attachment of the auxiliary filament to the wire 14.

The general heat within the bulb is not sufiicient to operate the strip I! and the strip ii is of such low resistance that the passage of current therethroug-h does not generate suifficient heat therein to actuate it.

In Fig. 5 is shown an arrangement in which the general heat within the bulb is utilized to make more positive contact between the strip ll and wire is when current is flowing through the auxiliary filament. In this arrangement, the strip H is twisted through 180 between its ends and is so arranged that expansion of the strip caused by the heat generated by the main filament at the point where the thermal metal is attached to its support tends to force the strip away from the wire W. The temperature acquired by the strip from general heat within the bulb causes the thermostat strip to be urged against the wire i! but at the temperatures acquired by the strip from heat supplied from the main filament is the greater of the two, and the thermostat strip bends out of con-tact with the wire l4. When the main filament burns out, the general heat within the lamp insures positive contact between thermal metal and support wire.

The thermostat strip I1 is of standard by-metal construction with one of the metals having a higher co-efiicient of expansion thanthe other. The strip is attached to the wire l3 with the metal of higher thermal co-efi'icient of expansion facing the wire. In the embodiment shown in Figs. 1 to 4, the metal having the higher coefficient of expansion engages the wire l4, while in the modification shown in Fig. 5, the strip is so twisted that the metal of lower co-ef'lcient of expansion engages the wire [4 when the strip is cold. In this modification, when the strip is heated, it first bends near its support to bring the metal of lower co-elficient of expansion out of contact with the wire l4 and then as the further end heats by general radiation and conduction it bends toward contact with the wire [4.

Thus when the first filament is burned out, no heat is generated at the support wire, the thermal strip l1 remains in contact with the wire M, and the general heat from the auxiliary filament causes the thermal strip [1 to be urged against its contact on the wire l4 thus reinforcing the contact at this point.

Referring now to Figs, 6 to 9 inclusive, the main filament extends between the upper ends of the leading-in wires l2 and I3 while the auxiliary filament 16 extends between the upper ends of the leading-in wires I2 and M. The strip I! of thermostatic material has a wire l8 welded to its upper end, the end of the wire in turn being welded to the upper end of the leading-in wire l3. A glass bead I9 is supported by the remaining end of the wire [8. A length of wire 20 is formed'intermediate its ends with a loop which is fused into the glass bead l9. One end portion 2| of the wire 20 extends to and is welded to the supporting wire M. The end portion 22 of the wire 20 is bent back on itself and to the top of the short leg is attached a plate 23 which is engageable with the thermostat strip [1. The plate 23 has a right angle extension 24 in which is provided a slot 25 through which extends the longer leg of the end portion 22. The end portion 22 is so tensioned that the shorter leg tends to move away from the longer leg, the extent of such movement being limited by engagement of the side of the slot 25 with the longer leg.

The arrangement is such that when no current is flowing in the lamp, the parts are in the position shown in Fig. 6 with the shorter leg of the end portion 22 in the closest relation to the longer leg permitted by the slot 25 and with the thermostat strip H in contact with the plate 23. Under such circumstances, the auxiliary filament is electrically connected to the leading-in wire 13 through the wire 20 and thermostat strip II. However, after a period of flow of current through the filaments, sufficient heat is communicated to the thermostat strip from the filament l5 so that the strip bends into the position shown in Fig.8. The plate 23 tends to follow strip I! under the influence of the tension in the end portion 22 of the wire 28 but its movement is arrested by engagement of the side of the slot 25 with the longer leg of the end portion 22 so that a gap is produced between the plate 23 and the thermostat strip H, thus breaking the electrical connection between the filament l5 and the supporting wire l3, thereby ole-energizing the filament It. This condition will be maintained so long as the main filament remains operative. Should the main filament become inoperative, then the thermostat strip will tend to return to its original position until it engages the plate 23 whereupon the circuit through the auxiliary filament I6 is closed and this filament is again energized. The general heat produced in the lamp by the filament IE3 may cause some bending of the thermostat strip I6 but will not cause sufficient bending thereof to move it away from the plate 23. The following movement of the plate 23 is sufficient to maintain it in contact with the strip l1 throughout the movement of it resulting from the general heat developed by the filament l5 and insures permanent closure of the auxiliary filament circuit after the main filament has become inoperative.

The wire l8, bead l9, wire 20 and plate 23 are independently assembled with the strip I1 and then this assembly is welded to the upper end of the supporting wire l3 and the end portion 2| welded to the supporting wire M. By reason of this prior assembly, the relation of the parts can be accurately established and it can be thus assured that they will function properly and that the relationship can be accurately reproduced in large quantities of these assemblies which constitute the switches for cutting in the auxiliary filament upon failure of the main filament. In this modification, as well as in the others, the strip I? is of such low resistance that substantial- 1y no heat is developed therein by passage of current therethrough. The strip I1 is responsive to heat communicated to it from the main filament rather to any internally developed heat resulting from the passage of current through it.

I claim:

1. In an incandescent electric lamp, a main filament and an auxiliary filament, supporting wires therefor, a switch comprising a strip of thermostat material fixed at one end to one of said supporting wires, an insulatingly supported resilient member located at the free end of said thermostat strip and being under tension to engage its free end with said thermostat strip, means for limiting the path of movement of the free end of said member, and an electrical connection between said member and another of said supporting wires.

2. In an incandescent electric lamp, a main filament and an auxiliary filament, supporting wires therefor, a switch comprising a strip of thermostat material fixed at one end to one of said supporting wires, an insulatingly supported resilient member located at the free end of said strip and being under tension tending to engage its free end with said thermostat strip, means electrically connecting said resilient member with another of said supporting wires, and means for limiting the path of movement of the free end of said resilient member.

3. In an incandescent electric lamp, a main lament and an auxiliary filament, supporting wires therefor, a switch comprising a strip of thermostat material fixed at one end. to one of said supporting wires, an insulatingly supported resilient member located at the free end of said strip and being under tension tending to engage its free end with said thermostat strip, means electrically connecting said resilient member with another of said supporting wires, an electrical conductor connecting said resilient member to another of said supporting wires, and means at the free end of said resilient member for engagement with said conductor to limit the path of movement of said free end of said resilient member.

4. In an incandescent electric lamp, a plurality of supporting wires, a main filament attached to one pair of supporting wires, an auxiliary filament attached to another pair of supporting wires, a switch comprising a strip of thermostatic material fixed at one end to one of the supporting wires for the main filament, an insulatingly supported resilient member located at the free end of said strip and being under tension tending to engage its free end with said thermostatic strip, and means for limiting the path of movement of the free end of said member.

5. In an incandescent electric lamp, a plurality of supporting wires, a main filament attached to one pair of supporting wires, an auxiliary filament attached to another pair of supporting wires, a switch comprising a strip of thermostatic material fixed at one end to one supporting wire for the main filament, an insulatingly supported resilient member located at the free end of said strip and being under tension tending to engage its free end with said thermostatic strip, an electrical conductor connecting said resilient member with a supporting wire for said auxiliary filament, and means at the free end of said resilient member engageable with said conductor to limit the path of movement of said free end.

6. In an incandescent electric lamp, a main filament and an auxiliary filament, supporting wires therefor, a switch comprising a strip of thermostat material fixed at one end to one of said supporting wires, an insulatingly supported resilient member located at the free end of said thermostat strip and being under tension to engage its free end with said thermostat strip, and an electrical connection between said member and another of said supporting wires.

,7. In an incandescent electric lamp, a plurality of supporting wires, a main filament attached to one pair of supporting wires, an auxiliary filament attached to another pair of supporting wires, a switch comprising a strip of thermostatic material fixed at one end to one of the supporting wires for the main filament, and an insulatingly supported resilient member located at the free end of said strip and being under tension tending to engage its free end with said thermostatic strip.

8. In an incandescent electric lamp, a plurality of supporting wires, a main filament attached to one pair of supporting wires, an auxiliary filament attached to another pair of supporting wires, a switch comprising a strip of thermostatic material fixed at one end to one supporting wire for the main filament, an insulatingly supported resilient member located at the free end of said strip and being under tension tending to engage its free end with said thermostatic strip, and an electrical conductor connecting said resilient member with a supporting wire for said auxiliary filament.

PAUL SCHWERIN. 

